The continued miniaturization of metal oxide semiconductor field effect transistors (MOSFETs) has driven the worldwide semiconductor industry. Various impediments to continued scaling have been predicted for decades, but a history of innovation has sustained Moore's Law in spite of many challenges. However, there are growing signs that metal oxide semiconductor transistors are beginning to reach their traditional scaling limits. Since it has become increasingly difficult to improve MOSFETs and therefore complementary metal oxide semiconductor (CMOS) performance through continued scaling, the development of advanced methods for improving performance, in addition to scaling, has become critical. One such method involves using high mobility materials, other than silicon, for CMOS such as Group III-V semiconductors or Silicon Germanium (SiGe) or Ge.
Methods for fabricating Fin structures (where the Fin can be composed of, for example, SiGe semiconductor material) are currently being explored. For the fabrication of Fin-based devices, where the unit cell or node geometry requires small dimensions, a Fin of a certain minimum required height (a vertical dimension relative to a surface upon which the Fin is disposed) can be required. However, for certain SiGe alloy compositions, as one non-limiting example Si1-xGex having a Ge percentage of, for example, 25% (i.e., x=0.25), a critical SiGe thickness can be in a range of about 30 nm to about 35 nm in a metastable state and about 10 nm in a thermal equilibrium state. However, such thicknesses can be less than a minimum required Fin height that is needed to achieve desired node dimensions. FIG. 1 is a graph that illustrates the critical thickness of Si1-xGex layers as a function of Ge mole fraction. The curves show a theoretic kinetic model for various growth temperatures (after J. J. Welser, The application of strained-silicon/relaxed-silicon germanium heterostructures to metal-oxide-semiconductor field effect transistors, PhD Thesis, Stanford University, 1994). The critical thickness is noted for the exemplary Ge mole fraction of 0.25.
It has been found that if the SiGe layer is formed with a thickness that is greater than the critical thickness for a particular Ge mole fraction then defects can be generated in the SiGe film or epilayer. The presence of such defects can be detrimental to subsequent device formation.
Clearly, a need exists to provide a method to form a substantially defect-free SiGe Fin having a height that is greater than the critical thickness for a desired Ge mole fraction.